1. Field of the Invention
The present invention relates to a car audio system, and more particularly, to an apparatus for improving an image in a car audio system, and a control method thereof.
2. Description of the Related Art
In recent years, as a car is presumed to be an essential means, various devices for providing various conveniences to a driver (for example, a car audio system) in addition to devices indispensable for running the car (for example, an engine) are being actively researched and developed.
Particularly, a digital car audio system for opening and closing a car door and receiving a music file by a cellular phone to reproduce the received music file through an audio device has been recently developed. The digital car audio system uses a digital intermediate frequency (DIF) method and a Bluetooth method being a standard of a local area wireless communication. In comparison to a conventional analogous car audio system, the digital car audio system is excellent in its performance of radio wave reception and reduces to the minimum an unnecessary noise or a multi-path phenomenon where radio wave is reflected in a downtown building jungle, thereby providing the best sound quality.
However, even the digital car audio system reduces a sound stage due to a characteristic of a listening space, that is, a characteristic of a car listening space. Then, the reduction of the sound stage depending on the characteristic of the listening space of the car audio system will be in detail described as follows.
First, unlike a general listening space, the car is greatly limited in its listening space and therefore, is being varied little by little for a condition of golden triangle partition. This is because, in a comparison of a ratio of a direct sound to an indirect sound, an excessive direct sound causes a user of the car audio system to easily feel fatigue and dislike and an excessive indirect sound causes the user to easily feel tight in listening to all music.
In general, keeping a reverberation time suitable to the listening space functions as an important factor in order to listen to the music. Reverberation is determined depending on a ratio where a sound is reflected in the listening space. Generally, a characteristic of a sound having a long reverberation time is called “live”, and a characteristic of a sound having a short reverberation time is called “dead”. There is a drawback in that a sound image becomes unclear when the live characteristic is great, and a music listening atmosphere is destroyed when the dead characteristic is great.
However, due to narrowness of the listening space, a listener of the car audio system is directly exposed to a speaker in the listening space of the car, and an echo sound and a reflection sound are reduced in level due to car interior materials and seat. As a result, an oriented direction and an angle of the speaker function as the most important factors in determining the sound stage of the car audio system.
However, a rear speaker is not only fixed but also reproduces only middle and low band sound in the car audio system, and therefore it is difficult to consider the live and dead characteristics of the reverberation. Accordingly, it is difficult to embody an accurate image depending on a position of the user of the car audio system, thereby making it also difficult to embody a Dolby digital surround sound in the car audio system.
Then, a general sound direction depending on a speaker position of the car audio system will be described with reference to FIG. 1.
FIGS. 1a and 1b schematically illustrate the sound direction depending on the speaker position of the car audio system.
In general, the car audio system includes a front speaker and a rear speaker. The sound direction based on a straightness of the high band sound and a permeability of the low band sound depending on the front speakers and the rear speakers is illustrated in FIGS. 1a and 1b. 
As aforementioned, the speakers of the car audio system are provided only at predetermined positions of a narrow car space and therefore, there is a drawback in that it is difficult to embody the accurate image depending on the user position, thereby deteriorating the sound stage.